Who?

It's Rick Perry, the rootin', tootin', coyote-shootin' Texan governor whose campaign appeared to ride off into the sunset only shortly after it had launched in a blaze of glory. It is hard to remember that Perry was seen as the dominant frontrunner just a few months ago. But, hang on, Perry is not the interesting bit of this ad. What is interesting is the target: Rick Santorum. Yes, the former Pennsylvania senator and rightwing social conservative (whose name should NOT be Googled) has finally hit the big time and earned himself an attack ad.

What?

A radio spot called "Game Show" (also released with simple video graphics online). Which means it is cheap. But radio matters in Iowa, especially perhaps in rural districts and with older voters.

When?

It went up on Thursday, perhaps finally turning Santorum's rise in the polls into an Official Anti-Romney Bubble. After all, it was his turn. The bubbles are coming thick and fast now. Newt Gingrich's second bubble seems to have fully burst, while Ron Paul's may be peaking. A Santorum bubble (again, for God's sake, don't Google that) was perhaps inevitable.

Why?

Beneath the nominal top tier of Mitt Romney, Newt Gingrich and Ron Paul there is a fierce battle going on among the also-rans of Perry, Michele Bachmann and Santorum (in Iowa, forget the moderate Jon Huntsman). The theory is that if one of those three manages to sneak into third place (likely edging out a fast-fading Gingrich), that will be a surprising enough development to merit a media narrative of a strong performance. That will propel the lucky candidate straight into New Hampshire. Currently Santorum, whose support has rocketed into the mid-teens in recent days, is looking the most likely to unexpectedly win third. So Perry has decided to attack him, delivering a massive backhanded compliment to Santorum in the process.

It is actually quite heart-warming. Whatever one thinks of Santorum's extreme social conservatism, he has toiled relentlessly in Iowa from small town to small town for months on end. No politician has worked harder in whatlooked an utterly hopeless cause. Now, with just days to go, he is finally part of the big picture.

How?

Santorum is the arch-social conservative of the race, with a solid record that appeals to the religious right. So, unsurprisingly, Perry has gone after Santorum on economic issues. Namely, he is seeking to paint Santorum as another part of the Washington establishment who has been irresponsible in encouraging government spending. He is doing this via the bizarre, and rather common practice, of "earmarks". This is where politicians will load up legislation with special treats (such as new factories, hospitals, tax breaks or roads) for their home states and districts in order to curry favour with the voters back home.

But, of course, while snagging millions for a new bridge in Alabama might win over voters in Birmingham, it tends to annoy the hell out of voters in Louisiana, Mississippi, and just about everywhere else. And vice versa. Virtually everyone does it in Congress and everyone hates it. So the radio spot takes the form of a mock game show, voiced by a smarmy-sounding host who goes under the moniker of Wink Taxandspend (hilarious!). It then goes on to ask mock questions about which politician approved a notorious "bridge to nowhere" earmark and who "demanded more than one billion dollars of earmarks in his 16 years in Congress"? The answer is the same: Rick Santorum.

In a special "audio bonus round", Santorum himself is then shown rather ill-advisedly boasting of his proud record of bringing home earmarks for his voters. "That's right, Iowa," Mr Taxandspend informs us at the end of the ad. "On taxes and spending, if Rick Santorum wins, you lose."

It is a good ad, hitting at a serious issue and a genuine weakness in a candidate whose appeal is out of synch in an election dominated by economic issues. But you know what? In Camp Santorum they will not care two hoots. They just earned an attack ad of their very own. It will be a wild party tonight at Santorum's headquarters. Or at least as wild as parties get when Rick Santorum and his merry band of conservative Christian followers are around.

More than $1bn will be spent on campaign ads in the 2012 race for the White House, as candidates woo voters in primaries and for the presidency: guardiannews.com commentators analyse the ads, decode the messaging and assess what truth there is in political advertising